1. Field of the Invention
This invention relates to the field of ridged waveguide antennas and particularly to double ridged waveguide antennas for microwave frequency communications. The disclosed antenna is intended for mounting in the boat tail of a missile.
2. Prior Art
The art and science of designing double ridged waveguide antennas for operation in the microwave frequency range are well understood for the conventional symmetric double ridged configuration. Extensive analysis and discussion are presented in a number of trade journal articles. Pertinent background information includes Properties of Ridge Waveguide appearing in the Proceedings of the I.R.E. of August 1947 at pages 783-788 authored by Seymour B. Cohn. This article makes it clear that ridged waveguide results in a lowered cutoff frequency, lowered impedence, and wide bandwidth free from high-mode interference when compared to nonridged waveguide. The usual geometry of the ridge is rectangular, although, as shown in a 1957 article by J. Van Bladel and O. Von Rohr Jr., semicircular ridges produce certain advantages desirable in some circumstances. See Semicircular Ridges in Rectangular Waveguides, appearing in the April 1957 IRE Transactions on Microwave Theory and Techniques. See also, "On the Complete Eigenvalue Solution of Ridged Waveguide" by James P. Montgomery appearing in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-19, No. 6, June 1971 at pages 547 to 555 and particularly FIGS. 7 and 8 which show non-symmetric ridges. A copy of each referenced article accompanies this application.
U.S. Pat. No. 4,245,222, Dual Function Antenna, issued Jan. 13, 1981 to Edward Eng et al. shows an antenna having a cavity shape similar to that of the present invention, as best illustrated in FIG. 4. Although the shape of the cavity is somewhat similar, it should be noted that the antenna is referred to as a circumferential slot antenna, having slots 22 and 24, and is not a ridged waveguide antenna. No ridges are present in the antenna of Eng et al. A copy of that patent accompanies this application.